Beam antenna



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BEAM ANTENNA I I Filed Nov. 30, 1951 INVENTOR l Vbodg ow Darling NEY 1 Patented July 27, 1954 BEAM ANTENNA Woodrow Darling, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 30, 1951, Serial No. 259,157

2 Claims. 1

This invention relates to the field of directional antenna systems and in particular to such a system having a very small back radiation.

It is known that in antenna systems, reflectors of different types are frequently used in short wave Work for obtaining concentration or beaming of the radiated energy or the received energy. It is further known that a given coaxial transmission line has a predetermined characteristic impedance at a particular operating frequency and, consequently, for maximum power transfer it is necessary that the antenna structure present a corresponding terminal impedance at the same frequency.

One of the important advantages of this invention lies in the high gain obtained by the novel arrangement of long radiators in conjunction with a reflecting screen whereby the lateral radiation lobes are canceled while a sharp forward lobe results.

A further advantage lies in the fact that no unbalance-to-balance feed unit is required to match the antenna system to the feed line.

This invention includes the use of two radiating elements and a reflecting screen. The elements cross at right angles at a fixed distance from the screen and from their free ends. Their other ends are supported at the screen. The radiating elements should be coupled to the feed line at the point where they cross. The impedance of this system can be adjusted to match the impedance of the feed line by changing the position of the crossover oint with respect to the screen.

It is one of the objects of this invention to provide a directional antenna system which has small back radiation.

It is a further object of this invention to provide a directive antenna system which has a wide frequency response.

It is yet another object of this invention to provide a directive antenna system which has a single feed point and an adjustable impedance so that no unbalance-to-balance feed unit is required.

These and other objects will be made clear when the following description is read in connection with the drawings in whichthe same numbers are used to refer to like parts.

Figure 1 is a perspective view of a preferred embodiment of my invention;

Figure 1a is a view partly in section looking in the general direction of arrow A of Fig. 1.

Figure 2 is a top view of Fig. 1;

Figure 3 is a top view of the insulating crossover spacer employed in Fig. 1; and

Figure 4 illustrates the radiation characteristic of the radiators 6 and 1 of Fig. 1.

It will be seen from Figs. 1 and 2 that there has been provided a pair of radiating elements, 6 and 7. These may be metal tubes or rods and should have a length of one and one-fourth of the length of the carrier wave in use. As will be shown, the use of tubes is preferable and they will be so referred to. These tubes are supported at one end by a reflecting screen, 5, and are so placed that they cross at right angles. The distance from their free ends to the point at which they cross should be nearly equal to 0.27 times the wave length in use. A feed line, I0, which has an inner conductor, II, and an outer conductor, l2, may be passed through one of the tubes, 6, and leave it at the point where the tubes cross. The tubes are insulated from each other at the crossover point by a spacer, 8, to which they are fixed by U-bolts, 9. The plane of the radiators, 6 and 1, is at right angles to the reflecting screen, 5. The screen should extend more than onefourth of the wave length in use beyond either side of the plane of the radiators. The distance horizontally between the centers of radiation is about one-half the wave length in use. The distance from the centers of radiation to the screen is about 0.45 the length of the wave.

The partial view, Fig. la, shows in detail the cross-over feed point. It is seen that at the point where the supply line, 10, leaves the tube, 6, the inner conductor, l l, of the line is bonded to the right radiator, I, and the outer conductor, I2, is bonded to the left radiator, 6.

In the preferred structure of my invention, the spacer, 8, as is shown in Fig. 3, is a square block of an insulating substance. A feed-thru hole is bored in its center through which the supply line passes. U-bolt holes are bored at each of its corners so that the tubes, 6 and I, may be clamped to the block.

For an understanding of how a directive radiation pattern is attained with this array, reference is made to Fig. 4 which illustrates the radiation pattern of radiators, 6 and l. The horizontal distance between the centers of radiation will be seen to be about one-half the length of the wave in use. The lobes, e and y, will be canceled out due to the fact that at all times they will differ in phase by degrees. The distance from the centers of radiation to the reflecting screen and back is equal to about 0.9 times the wave length. The lobes, f and h, traveling from the centers of radiation to the screen will reflect back from the screen and will add to the forward lobes. The

3 pattern that results will have a large forward lobe and little back radiation.

For example, if the center of each of the radiating arms is 0.437 wave lengths from the refleeting screen, the distance of travel of the wave to and from the screen is then 0.874 wave lengths corresponding to a 315 degree shift. The phase reversal at the screen contributes a 180 degree phase shift, so that the phase of the reflected wave at the center of radiation point is 135 degrees in relation to its original rearward direction. Since the phase of the lobes directed toward the reflecting surface is opposite in phase to the lobes leaving the radiators in the forward direction, the result is that the reflected wave front phase in respect to the forward lobe is 180 degrees plus 135 degrees:315 degrees or the phase difference is in effect 45 degrees from the forward lobe phase. Therefore, we have very nearly complete addition in the forward direction. The sharpness of the lobes as obtained by the long rods and cancellation of the lateral lobes maintains a high gain in the desired direction.

No extra feed unit is needed with this system to take care of an unbalance as to the antenna the radiators is about 0.27 wave length the input impedance will be fifty ohms; and if the distance from the feed point to the ends of the radiators is made more than 0.27 wave length, the resistance will be greater than fifty ohms. It is, therefore, a simple matter to match the array impedance with the transmission line impedance by adjusting the position of the feed point.

A variation of this antenna providing optimum addition of the forward lobes could be obtained by a slightly more complex design, which would remove the center of radiation to 0.75 wave length from the reflecting screen.

There have been shown what are now thought to be the preferred constructions of this invention. It will be clear to those skilled in the art that this system would operate equally as well if the plane of the radiators was rotated so that the polarization of the wave is other than horizontal, and that other changes may be made If the feed point without departing from the spirit of the invention.

I claim:

1. In an antenna system, the combination of a reflecting screen and a pair of radiators, said radiators projecting obliquely from said reflector so that the said radiators cross substantially at right angles at a predetermined distance from said reflector, a coaxial line having an inner conductor and an outer conductor passing through the first of said radiators and having its outer conductor electrically connected thereto at the point where the said radiators cross, the inner conductor of the said coaxial line protruding from the said first radiator and electrically aillxed to the second of the said radiators at said cross-over point, and means insulating said radiators from each other at the said cross-over point.

2. In an antenna system, the combination of a reflecting screen and a pair of radiating elements, said radiating elements having a length substantially equal to one and one-quarter times the length of the carrier Wave employed and lying in a plane perpendicular to the plane of the said reflecting screen so that the said radiators cross at approximately right angles at a distance from their free ends substantially equal to 0.27 times the said carrier wave length and having their other ends supported adjacent the said reflecting screen, said screen extending beyond the plane of said radiators a distance greater than one-fourth the said carrier wave length and extending beyond the supporting points of the said radiators a distance greater than oneiourth the said wave length, nonconductive spacers maintaining said radiators in spaced position, and a coaxial transmission line having an inner conductor and an outer conductor passing through the first of the said radiators, said outer conductor connected to said first radiator at the said cross-over point and said inner conductor protruding from th said first radiator at the point where said radiators cross and electrically bonded to the second of the said radiators.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,110,159 Landon Mar. 8, 1938 2,272,312 Tunick Feb. 10, 1942 2,434,893 Alford et al Jan. 27, 1948 2,485,138 Carter Oct. 18, 1949 2,562,296 Christensen et a1. June 31, 1951 

